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The WR and O-type star population predicted by massive star evolutionary synthesis
Evolutionary calculations of massive single stars and of massive closebinaries that we use in the population number synthesis (PNS) code arepresented. Special attention is given to the assumptions/uncertaintiesinfluencing these stellar evolutionary computations (and thus the PNSresults). A description is given of the PNS model together with theinitial statistical distributions of stellar parameters needed toperform number synthesis.We focus on the population of O-type stars andWR stars in regions where star formation was continuous in time and instarburst regions. We discuss the observations that have to be explainedby the model. These observations are then compared to the PNSpredictions.We conclude that: . probably the majority of the massivestars are formed as binary components with orbital period between 1 dayand 10 yr; most of them interact. . at most 8% of the O-type stars arerunaways due to a previous supernova explosion in a binary; recentstudies of pulsar space velocities and linking the latter to the effectof asymmetrical supernova explosions, reveal that only a smallpercentage of these runaways will have a neutron star companion. . withpresent day stellar evolutionary computations, it is difficult toexplain the observed WR/O number ratio in the solar neighbourhood and inthe inner Milky Way by assuming a constant star formation rate, with orwithout binaries. The observed ratio for the Magellanic Clouds is betterreproduced. . the majority of the single WR stars may have had a binarypast. . probably merely 2-3% (and certainly less than 8%) of all WRstars have a neutron star companion. . a comparison between theoreticalprediction and observations of young starbursts is meaningful only ifbinaries and the effect of binary evolution are correctly included. Themost stringent feature is the rejuvenation caused by mass transfer.
| UvbyHbeta_ photometry of main sequence A type stars.
We present Stroemgren uvby and Hbeta_ photometry for a set of575 northern main sequence A type stars, most of them belonging to theHipparcos Input Catalogue, with V from 5mag to 10mag and with knownradial velocities. These observations enlarge the catalogue we began tocompile some years ago to more than 1500 stars. Our catalogue includeskinematic and astrophysical data for each star. Our future goal is toperform an accurate analysis of the kinematical behaviour of these starsin the solar neighbourhood.
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